import pandas as pd

df1 = pd.DataFrame(
    [{"r1": 'a', "r2": 1.2},
     {"r1": "b", "r2": 2.3},
     {"r1": "c", "r2": 2.6},
     {"r1": "a", "r2": 3.0}
     ]
)

print(df1["r2"])
print(df1["r2"].floordiv(0.5)*0.5)
